Timechart how-to

Developer builds contain a performance analysis command called perf that can be used to create an SVG output file similar to bootchart; the chart shows how CPU cycles and I/O wait times are distributed across processes in the system over time.

Below is a short primer in four lessons describing how to generate and view output from perf timechart.

Lesson 1 - a simple example

Boot Chromium OS, and open a terminal.

Run this command:

sudo perf timechart record

Run your workload. A workload isn't necessary if all you want to see is a chart of an idle system. :-)

When your workload is done, interrupt the process started in step 2 using ^C, or kill -2.

Explanation: Without arguments, perf timechart record runs forever gathering data, until stopped by SIGINT. Note that only SIGINT works; SIGTERM will kill the process without producing the necessary output. When the command completes, you'll see two new files: perf.data and trace.out.

Lesson 2 - how to generate and view the chart

In the directory where you ran Lesson 1, run this command:

sudo perf timechart

The output image will be stored in a file named output.svg. Use scp or some equivalent to copy the file to another system for viewing.

Tips for viewing: Some browsers may have trouble displaying the image. The author of timechart recommends the Inkscape image editor:

Inkscape does a good job of displaying the fine details, but it may be a bit slow for the large timechart images. You should exercise patience when opening, magnifying, or scroling images.

Lesson 3 - how to avoid using SIGINT

Run this command:

sudo perf timechart record sleep 5

Run a workload that will finish within 5 seconds; for longer workloads, use a more appropriate sleep time in step 1.

Generate and view the output as described in Lesson 2.

Explanation: If there are arguments to perf timechart record, the arguments are treated as a command to run as a subprocess of perf. perf gathers data until the process terminates.

If your workload is triggered by a single command, that command can be used in place of 'sleep 5'. Note that if the workload acts as a daemon (that is, forks a child and exits), perf will terminate with the parent terminates; this likely isn't what you'd want.

Lesson 4 - how to get a timechart of system boot

Install bootchart on your workstation. For ubuntu:

sudo apt-get install bootchart

emerge and install bootchart onto your DUT:

emerge-$BOARD bootchart && cros deploy $DUT bootchart

reboot DUT

ssh $DUT reboot

bootchart will log events in /var/log/bootchart/boot-<timestamp>.tgz. It will collect data until the DUT upstart sequence has fully completed. Retrieve the archive(s) with